Vacuum technology is used extensively in the manufacture of semiconductor devices. One reason for this is that the components of an environment can be very closely controlled under very low pressures. In other words, by creating a vacuum and then creating a processing environment, such as by introducing a gas, the environment contains a very large percentage of the gas, and a very small percentage of any other constituents, known collectively as contaminants. In this manner, the materials being processed in the environments are exposed mostly to the gas that is introduced, and minimally to the contaminants.
In order to more tightly control the processes that are conducted within the vacuum equipment, it is desirable to gather certain information in regard to the process. Some of this information has to do with the process chamber itself, and other of the information has to do with the environment created within the process chamber. For example, the ability for a process chamber to maintain the vacuum that is drawn on the chamber is an important processing characteristic. If a chamber dissipates the vacuum too quickly, known as a high leak rate, then this situation introduces a relatively greater amount of contaminants into the chamber during a given period of time. At a certain point, a chamber with a leak rate that is too high is unfit to process semiconductor devices.
Further, it may be anticipated that during a portion of the processing of the semiconductor devices, a specific ratio of materials will be found in the effluent gases being drawn under vacuum from the processing chamber. If a different ratio is detected during processing, it might mean that there is something wrong with the process, or that the desired processing has been completed. In either case, this information is valuable to the process operator or process design engineer.
Many different types of instruments have been designed to detect the type of information described above, and many other types of information. These instruments typically operate by tapping into the process chamber in which the processing occurs, and on which the desired measurements are to be taken. Unfortunately, many process chambers are designed to remain at all times at a relatively low pressure, or in other words a relatively high vacuum, so that the chamber can be kept as free of contaminants as possible. Thus, repeatedly venting the chamber so as to insert and remove an instrument head from the chamber tends to degrade the cleanliness of the chamber, and is undesirable.
These test heads for the diagnostic instruments also create another problem. Many process chambers are designed to process a single wafer at a time, which tends to increase the uniformity of the processing across the wafer surface, and from wafer to wafer. Because of this design goal, the process chambers are relatively small. By tapping an instrument test head into the chamber, the volume of the process chamber is significantly increased. When the volume of the process chamber is altered in this manner, the process parameters themselves, such as residence time of any gases that may be introduced, are similarly effected. This creates a situation in which the reaction intended to occur within the process chamber may not proceed as anticipated.
What is needed therefore, is an apparatus for connecting a second vacuum apparatus to a semiconductor processing apparatus that does not require the chamber to vented when the second apparatus is connected and disconnected, and which does not appreciably alter the volume of the semiconductor processing chamber.